Relay stations (RSs) or Relay Nodes (RNs) have been proposed as coverage extensions in cellular systems. This recent development has triggered considerations of relays also in LTE. Thus, relaying has been proposed as a candidate feature for LTE-Advanced.
FIG. 1 illustrates a deployment scenario of a radio access network (RAN) with possible radio relayed extensions. Thus, FIG. 1 shows a communication system 100 that may comprise a user equipment (UE) 101 and a network (not shown). The communication system 100 may further comprise an evolved nodeB (eNB) 1021, which may provide access to the network, corresponding RNs #1 to #3 1022 connected to eNB 1021 via relay links (or equivalently backhaul links) and UEs 101 connected either to the RNs 1022 or directly to the eNB 1021 via access links.
As for the RNs 1022, apart from the main goal of coverage extension (shown at RN #2 1022), introducing relay concepts may also help in:                Provision of high-bit rate coverage in high shadowing environments (shown at RN #3 1022);        Reducing average radio-transmission power at the UE, thereby leading to long battery life;        Enhancing cell capacity and effective throughput, e.g., increasing cell-edge capacity and balancing cell load (shown at RN #1 1022); and        Enhancing overall performance and deployment cost of a radio access network (RAN).        
There are many kinds of relay systems proposed, starting from the simplest one such as amplify/forward (e.g. applied in single frequency digital video broadcasting handheld (DVB-H) networks, for example) ending up to the most complex one, which may utilize a network coding to improve overall performance.
In self-organizing networks (SON), handover thresholds, based for example on load measurements, are used. The handover decision e.g. in active mode may be effected according to the following equations:RS=Qmeas,s+Qhysts  (1), andRn=Qmeas,n−Qoffsets,n  (2),where Rs and Rn are the cell ranking for handover decision respectively in a serving/source cell s and in neighbor cells n; Qmeas,s and Qmeas,n are averaged signal measurements (e.g. reference signal received power (RSRP) or reference signal received quality (RSRQ)). However, the increase of the handover hysteresis QhystS or handover offset QoffsetS,n may cause the UE 101 to stay longer with the serving cell s.
Thus, the handover threshold setting may either delay or hasten the handover of a UE to a target cell. The handover procedure may remain the same as in the case of a network with no load balancing. That is, the load balancing may affect the handover process only indirectly by changing the values of the parameters, namely Rs and Rn, and the normal handover (i.e. handover in a network that does not consider load balancing) initiation, execution and finalization processes may remain valid.
In consideration of the above, according to examples of the present invention, a method, an apparatus and a related computer program product for load balancing are provided.
In this connection, the examples of the present invention enable one or more of the following:                Taking into account the load on the backhaul link by the handover decision, i.e. if a handover for the UE is to be effected towards the RN, taking into account that the UE will consume resources not only on the target RN-UE (e.g. access) link but also on the target eNB-RN (e.g. backhaul) link;        Coping with less information, i.e. the information on the load suffices, if the neighboring eNBs have information e.g. on the absolute number of resources. In that case, the number of residual resources may be derived (e.g. by multiplying total number of resources by (1-load)). Further, as for the coping with less information, e.g. the neighboring eNBs may not have information on the number of assigned resources e.g. for so-called backhauling, e.g. as a result of the resource partitioning.        Rendering the UE backward-compatible e.g. with legacy systems. In other words, from the UE's viewpoint, e.g. the serving network node (eNB or RN) could function in the same way as a legacy eNB;        Allowing users to benefit from relaying with legacy terminals. In other words, both legacy terminals and LTE-Advanced terminals can work equally well in legacy and LTE-Advanced networks.        Rendering LTE systems economically viable;        Keeping software and hardware updates between standard releases at the network side as small as possible;        Enabling the RN(s) to support main eNB functions. In other words, RN(s) is (are) capable of flexible resource sharing with a controlling eNB;        Enabling reduction of the serving/source cell load if overloaded;        Enabling adjustments of handover thresholds, thus controlling the handover offsets of the neighboring cells. Hence, both overloaded cells decreasing the offset and underemployed cells increasing the offset are taken into account. The offset may be negotiated between the two cells, i.e. the cell of interest may propose a new value (e.g. a step size can be defined) and the other cell may accept the value;        Having information that sufficient resources are available on the access link, while resources available on the backhaul link in the target cell may not be sufficient for supporting the UE;        Having information that sufficient resources are available also on “an almost congested” backhaul link in the target cell, and that the admission of the UE by the target RN (the admission may be decided by the target eNB) could decrease the average throughput that can be reached in the served area by the target RN;        Coping with resource partitioning not done properly, i.e. the target RN is congested not due to the access link but due to the backhaul link.        